altoslib: Delay accel cal value adjustment until data all read

altoslib: Delay accel cal value adjustment until data all read

Instead of trying to compute these values as soon as the necessary
data are available, delay until all data are available as which data
are necessary depends on the target device, and some target devices
don't have some of the data values at all.

Signed-off-by: Keith Packard <keithp@keithp.com>